Production of improved thioindigo pigments



Patented Jan. 3, 195% Y umreo STATES PRODUCTION or IMPROVED- 'THIOIN'DIGO PIGMENTS Donald Bernard Killian, Newark, N.J., assighior to I. I du Pont:de'f Nemours & Company,"Wilmington, 'Del., a corporation of Delaware No Drawing. QApplicationMarcli v, 1947, Serial No. 733,200

7 Claims. (015260 332) This "inventionrelates' to animproved process ;fonation-of the resultant dyestuff or' its interior produ'cing thio'indigolcoloring 'rnatters and mediates would oceur. The optimum temperature td=the products obtained'thereby. and reaction time vary, from case to casev depend- -It is anobjectof this invention to improve ing upon .the-naturetof the phenyl-thio'glycollic the process .of m'anufacturing certain types of ,acid-selectedas initial material.

thioindigo colors, "wherebyi'the='samemay be-ob- When the:phenyl-rthioglycollic acidis containedin a'form having superiortinctorial'quali- .densed .to the, corresponding thioindoxyl, and ties'to'those obtainedby hitherto known methods. when thelatteriisoxidized to the corresponding Othenand further. objects-of this invention will .thi'oindigo, water is evolvedias a by-product in appear as the description proceeds. ii:- the reaction. 'IYIhel water in turn reacts with the Thionaphthenx indigo dyestufis iand pigments, ,chlorosulfonic' acid 'toj 'yield sulfuric acidand hyhereinaf-ter caIledr-thioindigo coloring matters, drogen chloridejgas. fSulfur' dioxide is also evolved .h'averbeenin commerce-for 'many yearsas textile during the oxidation fphas'e lot the. reaction. dyes. This classofdyestufi coversa wide; shade Thi'oindigo'formationtis complete when no more 'rangeand; fromthe viewpoint of chemical struc- 1:) hydrogen.chlorideoaiidjsiiliurrlioigideare evolved. -turei-eomprises 2':2--bisthionaphthenindigo (Col At this 'stagein the. processjthevdye tuffi isdisour: Index #l 207) =and-its-substitution products. solvedin'the mixture of'chlorosmfonic acid and -A-number-of red-and 'maroon'thioindigo'colors sulfuric acidv resulting. from the'rea ction. "The have gained wide usage in-thepigment field-in pigment colorisf obtained by drowning the above -=recent-years; particularly inthe formulation of .120 .solution inwatrf by anybfthej methods known durable automotive finishes and other -paints to'jthe' art; andipref erlably by the turbulent-flow where good durability and light-fastness are reprocess"described'inDetrick and Brandt, 'U. S;P. quired. 2,334,812. :Thejprecipitated'pigment is filtered, --Severa1' convenientmethods forrsynthesisof washed; andmay'be dried or-kept' as press-cake rthioindigo--dyes are known in the art; ne-'-of\,25"pu1p. .The resultant colorsiwhen ldispersed in -the-most importantwornprising ring closure.of a lithographic' varnish; or paint vehicle,- by conr an appropriate phenyl-thioglycollic acid "in a ventional 'means'arestronger and more intense, strong-1ydehydratingimineral acid-such as oleum and different in shade than similarpigmentspreor chlorosiilfonic aeid,:- to -.-the corresponding paredwithouttheniercaptan. thioindoxyl, -followed byoxidation in-situ-tothqwo ,As typical or commerciallyconvenientphenyl- .thioind-igo, as-described -f0rinstance by Schmidt thioglycollic waster-mam m invention, may and -Bryk-in U. S.- Patents-Nos. 916,029 and be mentioned;-4 chloro-phenyl thioglycollicacid; 916,030. For-example, ring-closure and oxidation 3':4 dichlorophenyl-thioglycollic acid; Z-me'thylof-- 2wmethyl-4- chlorophenyl thioglycolliceacideto 4 'chloro bhe r th io'g- -vcoll ac d; 2 e'thy the corresponding 5 5. dichloro 7:7 dii-methyl- 3-c b fl p y g y zi3-dimethylthioindigo occurs readilydn cold chlorosulfonic Qch loro -phenyl-thiolycollic acid; 2 4f5-trich1oroacid, and the resultantapigment .dyestufids a --phenyl thioglycollic iacidifl m'e'thyl--brornomaroon pigment of considerable. (commercial p l yl d' y i a 2 y 4 value... I have now found that addition of. organic phenybthioglycollic acid. .merc aptans or disulfides'to thefchlorosu'lfonic 40 As-sli able Organic?mercalitansiusablein the acid; prior to ringeclosure. and ioxidationof a novelprocessmaybenamed: n-butyl"mercaptan; 'fphenylthioglycol'lic acid tow the corresponding iso-butyl- 'mercaptan; H-amyI'SmerCa'ptan;n=octy1 "thioindigo, gives'pigments of valuable andnnrnercaptan; n-d'od'ecyl:rmercaptan; pinenermerexpectedly superior tincto'rial properties comcaptan; tricnloro hiophenoh' 3:4 dim'ethylpared to the same colorsmade withoutjthe; added i0heny1 mercaptan; .4 adimethyl -'phenyl merorganic mer'captan orits' derivatives. 'cap'tan; 3-mercaptobenzoic acid;i 4-'mercaptoben- Accordingly, my'invention comprises a process z'o'ic acid; 2=mercaptobenzoiezaeid *for'p'rducing'ithioindigo coloring matters by sub- In summary, it seems that any alkyl; aryli'or jecting a phenyl-thioglycollic acid to ring-closure 'terpenei mercaptan or'r 'any compound. which refand oxidation in a strongly mineral, acid hay-T 5 sults'zfrom'sucnaamercaptan when the"latter'iis i -m oxidative i properties, suchsulfuric acid, -=subjcted=t0 I mild-oxidizing:conditions in-an acid oleum or .chlorosulfonic acid, the. reactionmass rmedium;forrinstanceithe' corresponding disulfide, containing further anorganic ,mercaptan.or.=.-its -issuitablei-for:-my-invention. the'a-bove list f'eiquivalent' such. as the-corresponding.disiilfide. "Sh0WS,' th6 initial smercaptan maysbe of an-ali- .Morer particularlyr inj'the.preferredhpractice of'1;55' phatic,-aromaticor-terpenenature; and it may my invention; a phenyl'thioglycollic acid is added 4 car-rviinert substituentssuchashalogenor'lower with good agitation to'asolution" or mixture of fialkyl. Of--spec-ial interest, :however, are those an organic mercaptanin chlorosulfonic acid at a compoundswhieh 'contain -water--so1ubilizingv or -temperaturuhigh eneugh for --reactionwto z the -alkali -",so1ubilizing-agroups,- :as typified by the zthioin'di'gmbut belowsthat:temperature where; sulmercapto-benzoic-aeids abovenamedy-iordn this instance, the mercaptan or its resultant acidoxidization product is readily washed out of the final pigment by treatment with water or dilute alkali.

The invention will now be illustrated in detail by the following specific examples, which however are not to be construed in a limiting sense. Parts mentioned are by weight.

Example 1 A four-neck flask, equipped with an agitator,

thermometer, calcium chloride drying tube, and.

charging funnel is charged with 315 parts of chlorosulfonic acid. The agitator is started, and the flask contents cooled to -5 G. externally, by immersing the flask in an ice bath. A solution of parts of n-dodecyl mercaptan in 80 parts of carbon tetrachloride is added slowly, and the solution is stirred to a temperature of 5 C. Thereafter, 100 parts of commercial-grade, 2- methyl-4chloro-phenyl-thioglycollic acid (prepared by the method of Schmidt and Bryk U. S. P. 916,029) are added in about equal portions over a period of 30 to 45 minutes. After each addition of the phenyl-thioglycollic acid, the temperature in the flask rises to 10-l2 C.; stirring is continued after each such addition (of intermediate) until the temperature drops to 5-8 C. before addition of the next portion. When all the 2-methyl 4-chlo'ro-phenyl-thioglycollic acid is added, the charging port is closed, and the solution is stirred for one hour permitting the temperature to rise gradually to 12 C. in that time. Vigorous evolution of hydrogen chloride and sulfur dioxide occurs during the charging and reaction cycles. Thereafter, stirring is continued for 3 hours until no more hydrogen chloride is evolved from the reaction. During this time the temperature is permitted to rise to 17-20 C. The resultant product is a dark green solution of dyestuff in a mixture of chlorosulfonic acid and sulfuric acid (the latter having been formed by hydrolysis of chlorosulfonic acid with the water evolved in the reaction).

The above dyestuif solution is drowned in water under conditions of high turbulence, using the method of the Detrick and Brandt U. S. Patent 2,334,812. The colorin matter, 5:5'-dichloro- 7:7 dimethyl 2:2 bisthionaphthenindigo, is precipitated as a dark red or maroon pigment. The thioindigo pigment slurry is filtered, washed acid-free, reslurried in 2% caustic soda, and heated to 80-90 C. for one hour adding a dilute sodium hypochlorite solution, as required, to maintain a slight excess of hypochlorite ion in solution. The extracted pigment is filtered,

washed alkaline-free, and dried at 60 C. The

dried color is a bright maroon powder.

In one of my experiments as above, I made a control run exactly as in the above procedure, but omitting the n-dodecyl mercaptan from the reaction.

The two products were dispersed in an alkyd enamel by conventional means both in full shades and extended with a prime white pigment such as antimony oxide or titanium dioxide. The enamels were sprayed on steel panels to give a film sufiiciently thick for complete hiding, and air dried for one day. Tinctorial comparison of the dried panels showed the pigment made with n-dodecyl mercaptan to be intense and very light in masstone, and intense, yellow and strong in tint compared with the control sample made without the n-dodecyl mercaptan.

4 Example 2 The process of Example 1 is followed except using a purified form of 2-methyl-4-chlorophenyl-thioglycollic acid made by the process referred to in Example 1, and purified by solution in dilute sodium carbonate followed by treatment with decolorizing charcoal, filtration, reprecipitation of the acid in the clarified filtrate with 10 dilute mineral acid, filtering, washing, and drying. The resultant thioindigo pigment compared in an alkyd enamel system to a control product made from the same purified 2-methy1- 4-chloro-phenyl-thioglycollic acid is very light and intense in masstone'and very yellow, strong and intense in tint compared with the latter.

Analysis of the pigment made with n-dodecyl mercaptan for sulfur and chlorine gave 16.29% sulfur and 17.20% chlorine. The control sample made without mercaptan analyzed 16.13% sulfur and 17.71% chlorine. These results indicate that part, if not all, of the n-dodecyl mercaptan is retained in the final pigment, most likely in the form of an insoluble di-dodecyl disulfide or a derivative thereof.

If the above process is repeated using only 2.5 parts n-dodecyl mercaptan per 100 parts of purified 2-methyl-4-chloro-phenyl-thioglycollic acid, a pigment is obtained intermediate in masstone depth in enamel between the one made with 5% n-dodecyl mercaptan and the control product made without mercaptan. However, the tint of the pigment made with the lower amount of the mercaptan is intense, yellow and strong compared with the control sample made without mercaptan.

Example 3 The reaction flask of Example 1 is charged with 612 parts of chlorosulfonic acid, and 10 parts of 3-mercapto-benzoic acid. The mixture is stirred and cooled to 5 C. Thereafter, 200 parts of purified 2-methyl-4-chloro-phenyl-thioglycollic acid of Example 2 are charged in small portions so that the temperature of the reaction mixture does not rise above 12 C. Thereafter, the reaction is finished and the pigment precipitated by drowning in water as described in Example 1. In one of my experiments, a control sample, run in the same way but without 3-mercapto-benzoic acid, was alsom'ade.

The finished pigments were dispersed in lithographic varnish or an alkyd enamel, and compared tinctorially. The product made with 3- w mercapto-benzoic acid was very intense and light in masstone and yellow, strong and intense in tint compared with the control sample made without the mercapto-benzoic acid.

Analysis of the two pigments above for sulfur 60 and chlorine gave the following results:

These results indicate that most, if not all, the 3-mercapto-benzoic acid is removed from the finished-pigment during the washing and alkaline extraction steps in the process.

Example 4 p A reaction flask equipped as described in Example 1 is charged with parts of chlorosulprocess of -Earanriple 'Twas' repeatedexwas prepared in a similarumanner but'without ,gfflfldBaEWith -tnicmordl-ithioplrenol fi e werymthe u f-t e capt nz imac dk tensemndiughtzinmasstoneiand yeuow, 'stro'iis H Ewmbleiy sand ihtenseon :tinfieompareditoiithe'control sampie made without the trichloro-thicphenol. A appar us. as in a p 1 was charged It will be clear that the above examples are v With 160 Parts Of ChlOrOsulfOnic c The merely illustrative, and that the details of protator was started, and the flask contents were 70 d re may be varied within wide limits. Thus, c l extel'nally y immersing the the conditions for ring-closure of the selected flask in an icebath. While stirring, 2.5 parts phenyl-thioglycollic acid, and oxidation of the of diphenyl disulfide were added slowly. Thereresultant thioindoxyl to a pigment may vary after 50 parts a of purified 2-methyl-4-chloroconsiderably in optimum temperature for the rephenyl thioglycollic acid were added in about 10 76 action, time of reaction, and in the ratio of vthe phenyl-thioglycollic acid to thedehydratlng mineral acid used, as illustrated in the six preceding examples above. Likewise, the choice of reaction medium, and dehydrating acid used may be varied, depending on the nature of the .phenyl-thioglycollic acid started with. For instance, some substituted phenyl-thioglycollic acids may be satisfactorily reacted with strong sulfuric acid, others with mixtures of sulfuric acid and chlorosulfonic acid, and others in straight chlorosulfonic acid or oleum. Also, it

.may.be preferred in some cases to oxidize the thioindoxyl intermediate in a separate reaction eitherbefore or after separation from the mineral acid in which it was formed. All such variations are, however, well known to those skilled in this art, and are within the spirit and scope of this invention.

In-place of the organic mercaptans mentioned above for use in the process of this-invention, the corresponding disulfides may be employed.

Thechoice between the two types of agent will generally be determined by the ease of preparation or more ready availability of one type or the other. The mercaptans or their equivalent disulfides may be added to the reactionmass in amounts varying from 1 to 20% by weight of the entering phenyl-thioglycollic acid, but the preferred proportions are from 2 to 10%.

The mechanism of the reaction whereby the organic mercaptans operate in the synthesis of thioindigopigments as described above to yield tinctorially difierent and more valuable thioindigo pigments is not understood. However, while I do notwish to be bound to any theory of reaction mechanism, observation of the reaction indicates that a more rapid ring-closure and oxidation of aphenyl-thioglycollic occurs in the presence of an organic mercaptan, which facts suggest that the latter compounds may function as oxidation promoters in the reaction.

The advantages and merits of my invention will now be readily apparent. Preparation of thioindigo pigments by the processes heretofore known to the art gives, in the case of any specified thioindigo, made under controlled conditions, a product of definite tinctorial properties such as masstone, shade and strength in paints, plastics, lithographic inks, etc., which properties cannot be altered significantly by customary variations in the process. The process of this invention provides unexpected, novel and different pigments in their tinctorial properties which properties have not been obtained in prior art processes. Thus, 5 5'-dich1or-7 i'-dimethyl-2 :2'-bisthionaphthenindigo prepared by the usual process known in the art without addition of an organic mercaptan is a maroon pigment, of a rather bluish red shade in tint, and somewhat dull both in full shade and tint when dispersed in systems such as plastics, lithographic inks, and paints. But the same pigment when prepared in the presence of an organic mercaptan is a brighter, yellower, and more desirable maroon in both masstone and tint andmoreover posierties are valuable and highly; desirable, and have heretofore been unobtainable with this color by known processes.

This invention, therefore, provides a simple and readily applicable means of altering the tinctorial properties of thioindlgo pigments from those obtainable'heretofore. The products of this invention are novel, and more desirable tinctorially than those from prior art processes, and, furthermore, are valuable commercially.

The pigments to which this invention relates are applicable widely in the arts for coloration of plastics, paper, leather, textiles, paints, and in the lithographic arts.

I claim as my invention: 1. In the process of preparing a thioindigo coloring matter by reacting with a dehydrating and oxidizing mineral acid upona phenyl-thioglycollic acid, the improvement which consists in effecting the reaction in the presence of-a compound selected from the group .consisting of organic mercaptans and disulfides. v

2. In the process of preparing a thioindigo coloring matter by successive ring-closure and oxidation of a phenyl-thioglycollic acid by the aid of chlorosulfonic acid, the improvement which consists in effecting the reaction in the presence of an organic mercaptan.

3. In the process of preparing a thioindigo coloring matter by reacting with a dehydrating and oxidizing mineral acid upon a phenyl-thioglycollic acid, the improvement which consists in efiecting the reaction in the presence of an organic mercaptan which carries a water-solubilizing radical.

4. In the process of preparing a thioindigo coloring matter by reacting with a dehydrating and oxidizing mineral acid upona phenyl-thioglycollic acid, the improvement which consists in efiecting the reactionin the presence of an organic mercaptan possessing a COOH group.

sesses greater tinting strength than the pigment made without mercaptan. These improved prop- 5. The process of preparing 5:5'-dichloro-7:"7"- dimethyl 2:2 bisthionaphthenindigo, which comprises reacting with chlorosulfonic acid upon 2-methyl-4-chloro-phenyl thioglycollic acid in the presence of an alkyl mercaptan.

6. The process of, preparing 5:5'-dich1oro-7 :7- dimethyl 2:2 bisthionaphthenindigo, which comprises reacting with chlorosulfonic acid upon 2-methyl-4-chloro-phenyl thioglycollic :acid in the presence'of a dimethyl-phenyl mercaptan.

7. The process of preparing 5: '-dichloro-7:7' dimethyl 2:2'-- bisthionaphthenindigo, which comprises reacting with chlorosulfonic acid upon 2-methyl-4-chloro-phenyl thioglycollic acid in the presence of a mercapto-benzoic acid.

DONALD BERNARD KII'JLIAN.

I REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Number 

1. IN THE PROCESS OF PREPARING A THIOINDIGO COLORING MATTER BY REACTING WITH A DEHYDRATING AND OXIDIZING MINERAL ACID UPON A PHENYL-THIOGLYCOLLIC ACID, THE IMPROVEMENT WHICH CONSISTS IN EFFECTING THE REACTION IN THE PRESENCE OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ORGANIC MERCAPTANS AND DISULFIDES. 